Fire protection nozzles are used to discharge water, with or without additives, in a relatively fine spray, which is generally referred to in the industry as mist. In contrast, fire protection sprinklers discharge water as a spray of large droplets or streams of water. The fire industry further distinguishes water discharging fire protection devices as being either nozzles or sprinklers based upon the device satisfying an industry accepted performance standard. For example, devices satisfying performance test specified in Factory Mutual (FM) Global Technologies LLC publication, Approval Standard For Water Mist Systems: Class No. 5560 (May 2005) (hereinafter “FM 5560”) are classified as water mist devices or nozzles.
The mechanism(s) by which a fine spray (water mist) acts to control, suppress or extinguish a fire can be a complex combination of two or more of the following factors, depending on the operating concept of the individual nozzle, the size of the orifice(s), the diffuser element, the operating pressure and flow rate:
1. Heat Extraction from the Fire as Water is Converted into Vapor
The amount of evaporation and hence heat withdrawn from the fire (i.e., cooling of the fuel) is a function of surface area of water droplets applied, for a given volume. Reducing droplet size increases surface area and increases the cooling effect of a given volumetric flow rate of water.
2. Reduced Oxygen Levels as the Vapor Displaces Oxygen Near the Seat of the Fire
When water converts to vapor, it expands by a factor of about 1650 times, displacing and diluting oxygen, thereby blocking the access of oxygen to the fuel.
3. Deluging of the Protected Area
Small water droplets are extremely light, and tend to remain suspended with the slightest air currents. This results in a “mist” that tends to distribute itself throughout an enclosure, outside of the direct spray range of an individual nozzle. Fine water droplets are, therefore, more likely to be drawn into the seat of the fire, further enhancing the effectiveness of the systems. This three-dimensional effect of the mist distribution also acts to cool the gases and other fuels in the area, blocking the transfer of radiant heat to adjacent combustibles, as well as, pre-wetting them.
4. Direct Impingement Wetting and Cooling of Combustibles
In addition to the pre-wetting and cooling of the flames by vaporizing water droplets, fire extinguishment by direct contact of the water droplets with the burning fuel to prevent further generation of the combustible vapors is one of the modes of addressing a fire and more preferably controlling a fire normally associated with traditional sprinklers. However, with a fast response release mechanism, high momentum mist can be effective in this mode during the early development stage of exposed fires.
A known fire protection nozzle is shown and described in U.S. Pat. No. 5,392,993. Another type of known fire protection nozzle is shown and described in International PCT Patent Publication WO 98/18525. Other known fire protection nozzles are the AquaMist® nozzles from Tyco Fire Suppression & Building Products of Lansdale, Pa. (hereinafter “Tyco”). For example, the AM4 and AM10 AquaMist® nozzles were developed for the special hazards market, a segment of water spray fire protection very different than sprinklers. These nozzles provided extinguishment of Class B (flammable liquids) fires via total flooding deluge protection of machinery spaces. Other complementary AquaMist nozzles were also developed during this time period: the AM6, AM11, AM22 and AM24 nozzles were developed with International Maritime Organization (IMO standard IMO A.800(19) marine system and, later, the AM15 nozzle was developed with the IMO System 913 local application system. Previously published data sheets for each of the AM4, AM6, AM10, AM11, AM22, and AM24 nozzles and patent publications are U.S. Pat. No. 5,392,993 and WO 98/18525 are included in the U.S. Provisional Patent Application No. 61/193,873.
The AM24 nozzle was tested separately by Underwriters Laboratories for its potential to protect up to Ordinary Hazard, Group 2 (OH2) occupancies as defined in National Fire Protection Association (NFPA) publication entitled, NFPA 13: Standard for the Installation of Automatic Sprinkler Systems (NFPA 13). An AM24 arrangement was tested per UL 2167 and was found to successfully pass rigorous OH2 fire testing. The nozzle received a UL listing according to this protocol. Due to the relatively small diameter spray pattern that is characteristic of the nozzle, the listing only allowed for installations at relatively limited nozzle spacings and ceiling heights. Although fire test requirements for Light Hazard (LH) and Ordinary Hazard, Group 1 (OH1) (as defined by NFPA 13) were less severe, the AM24 had been designed for OH2 testing. The resultant installation parameters for LH and OH1 suffered the same fate, and only a small ceiling height concession was allowed.
Summarized below in the tables below are known prior AQUAMIST® Nozzles showing their installation parameters for various hazards. For each nozzle the table indicates the K-factor (in gpm/psi 1/2) the minimum operating pressure, the maximum spacing of the nozzle, the coverage area per nozzle, the effective flux density, i.e., the flow delivered per square foot by the nozzle and the maximum ceiling height under which the nozzle may be installed.
TABLE AClass A firesAM6(LH Commodity)k0.33[gpm/psi{circumflex over ( )}½]min. pressure116[psi]Max. spacing5′10″max. area26[ft{circumflex over ( )}2]eff. flux density0.137[gpm/ft{circumflex over ( )}2]max. ceiling height8′2″
TABLE BClass A firesAM11(LH Commodity)K0.33[gpm/psi{circumflex over ( )}½]Min. pressure102[psi]max. spacing8′2″max. area67[ft{circumflex over ( )}2]eff. flux density0.050[gpm/ft{circumflex over ( )}2]max. ceiling height8′2″
TABLE CClass A firesAM22(LH Commodity)k0.64[gpm/psi{circumflex over ( )}½]min. pressure102[psi]Max. spacing11′6″max. area132[ft{circumflex over ( )}2]eff. flux density0.049[gpm/ft{circumflex over ( )}2]max. ceiling height8′2″
TABLE DClass A firesAM22(LH Commodity)k0.64[gpm/psi{circumflex over ( )}½]min. pressure102[psi]max. spacing9′2″max. area84[ft{circumflex over ( )}2]eff. flux density0.077[gpm/ft{circumflex over ( )}2]Max. ceiling height16′5″
TABLE EClass A firesAM24(OH Commodity)k0.64[gpm/psi{circumflex over ( )}½]min. pressure102[psi]max. spacing8′2″max. area67[ft{circumflex over ( )}2]eff. flux density0.096[gpm/ft{circumflex over ( )}2]max. ceiling height8′2″
To date, it is believed that standard setting organizations have maintained that water mist systems are to satisfy the hydraulic design criteria the greater of nine nozzles or 1500 square feet as specified by standard setting organization such as for example, Factory Mutual (FM) Global Technologies LLC or NFPA. The amount of water discharged during system operation is one of the primary concerns of water mist system designers. This is typically based on the goal of preserving the interior finish of a building or the items contained within (i.e. priceless paintings). Another goal may be providing adequate fire protection in a building with a limited volume of water. Either way, water supply can be a primary concern in choosing a water mist system over a sprinkler system.